1. Field of the Invention
The invention relates to periscopes for observing an exterior field of view from within a protected structure, and particularly, to a periscope for armored vehicles. More particularly, the invention relates to a periscope having an optical system with a beam splitter in order to provide a pair of observer viewing windows with only a single external object viewing opening.
2. Description of the Prior Art
Numerous periscope constructions have been developed and are in use for armored vehicles such as tanks. These periscopes contain various optical systems which enable an occupant to observe a field of view exterior of the vehicle without providing a direct opening through the armor for passage of projectiles, chemicals, liquids, or other harmful materials. Many periscope constructions presently used on tanks consist of a single or a pair of solid plastic prismatic-shaped blocks mounted within a protected housing which extends through an opening in the tank. The tank occupant or observer views the exterior field of view through a single external viewing window opening and a single observer window opening located on diagonally opposite ends of the optical system housing.
It is desirable for some applications to have a pair of observer viewing windows or ports instead of the usual single observer opening for use by occupants of the protective structure or vehicle. The only know periscope constructions which have more than a single observer viewing opening use a movable mirror or mirrors for changing the direction of the light beams after they enter the optical system of the periscope. Any armor vehicle periscopes having movable parts such as mirrors, encounter serious problems in that the harsh environments to which they are subjected result in vibrations and distorted viewing to an observer and various maintenance problems. Likewise, manual manipulation is required for changing the viewing image between the pair of observer viewing windows. Also, only a single occupant can view the external field of view at one time and does not permit simultaneous viewing thereof by both occupants.
Therefore, the need has existed for a periscope construction for use in an armored vehicle which has at least a pair of observer viewing windows, at least one of which is located within the protected vehicle and which has only a single external field of view window opening; and in which the periscope is free of movable parts or other components which are subject to breakage and maintenance problems.